Trimble gives as his reasoning the settlement of the constitutional issues and a desire to be more involved in national politics. He also has this to say on the issue of giving Northern Ireland a greater say in UK wide politics:

I know from my experience in the Commons that a handful of opposition backbenchers rarely have enough influence. My move today will not change that. But my move draws attention to my view that the people of Northern Ireland will need to have more influence and can only really do so if they are more fully involved in the national politics of the United Kingdom. This would require a direct link to the major parties of the State, namely, in alphabetic order, the Conservatives, Labour, and the Liberal Democrats. For parties are the life blood of British Parliamentary democracy.

This would mean some form of realignment bringing all the national parties to compete for the votes of the people here. Part of that realignment could be the recreation of the historic relationship between the Conservatives and the Ulster Unionists. But as the experience of the Northern Ireland Conservatives has shown, realignment cannot be achieved by one party alone. We need Labour and Liberal Democrats to be equally involved. Consequently I have not tried to persuade individual Ulster Unionists who intend to remain active in Ulster politics to follow me as individuals. But I do want to persuade the Ulster Unionist Party, and others, to integrate themselves more fully into British politics.

Whether his words will be heeded in all three parties remains to be seen, but it has become increasingly clear that right-centre-left politics requires all three parties involved. (A rare kudos to the Greens for at least bringing a serious side option.)

As for Trimble himself, I believe history will ultimately vindicate him. It is highly telling the way that all parties, especially the DUP, have moved over the years towards a system of constructive engagement. And the Union is far safer today than it was in past decades when the future of the province was deeply uncertain, when parties on all sides sought to end any attempt at progress increasing the attractiveness of an end to the Union. The principle of an internal settlement within the province within the UK has been accepted. As the institutions of government get into full speed, the "if it ain't broke don't fix it" position will set in. What was the Good Friday Agreement if not a victory for the Union?